1. Field of the Technology
The present invention relates generally to mobile stations operating in wireless communication networks, and more particularly to mobile station scanning methods and apparatus which utilize a carrier signal bandwidth test.
2. Description of the Related Art
A mobile communication device, such as a mobile station operating in a wireless communication network, may provide for both voice telephony and packet data communications. A mobile station may, for example, be compatible with 3rd Generation (3G) communication standards (such as IS-2000 Release 0) and utilize Global System for Mobile Communications (GSM), Time Division Multiple Access (TDMA), or Code Division Multiple Access (CDMA) wireless network technologies.
All of these communication system technologies utilize radio frequency (RF) signal detection techniques. GSM-based systems operate in the 850 Megahertz (MHz) band (869.2-893.8 MHz) in North America, Central America and some countries in South America. In a given region, other communications systems such as paging, digital advanced mobile phone system (DAMPS), and Mobitex systems, may also occupy bandwidth in the 850 MHz band. In this RF band, the assigned channels for GSM-based systems in each geographical region are different from those of its neighboring region and usually different than those of most nearby regions.
In an RF receiver, a scanning process exists for the purpose of detecting each RF carrier signal in the RF band and decoding channel information over the control channels of the networks associated with the RF carrier signals. The scanning process obtains channel information from the base station's signal, and then adds the channel information, along with the RF carrier information, to a channel list for a particular region. The construction of a channel list occurs whenever a mobile station exits one region and enters another region, or when the mobile station is powered on.
In GSM-based systems, information that is detected over the control channel during the scanning process includes a frequency correction channel (FCCH) burst or signal. The FCCH signal is a frequency correction signal which provides a GSM mobile station with a frequency reference in order to synchronize with the GSM network. Although non-GSM base stations transmit RF carrier signals on RF channels of the “GSM band,” non-GSM base stations do not broadcast any FCCH burst. Note that the non-GSM RF signals may in fact be considered top GSM candidate signals during scanning, as they may have been observed to be stronger than GSM RF carrier signals. In any case, a GSM mobile station will ultimately reject the non-GSM RF signal and refrain from including the RF channel in the channel list.
However, the FCCH detector requires at least eleven (11) frames (50.8 milliseconds) to reject the non-GSM RF signal due to the recurrence of frequency correction burst information. This is a relatively long time. Per GSM-based standards, a GSM system must be acquired within five (5) seconds. This may be difficult to consistently achieve in the 850 MHz band unless some special scanning techniques are utilized.
Accordingly, what are needed are methods and apparatus for quickly scanning an RF band so as to overcome the deficiencies in the prior art.